Electromagnetic control system



A A. THOMAS ELECTROMAGNETIC CONTROL SYSTEI Original Filed March 20, 1924 IINVENTOR Patented Sept. 2, 1930 PATENT QFFICE ADOLPH A. THGTEAS, OF NEW YORK, N. Y.

ELECTROMAGNETIC OOHTBOL SYSTEM Application filed March 20, 1524, Serial No. 700,537. Renewed March 8, 1930.

My invention relates to electric control apparatus which, in one aspect of my invention, is capable of amplifying the effects of variable electric currents to produce or cause mechanical operations which the currents might otherwise be too feeble to bring about. As will appear later, my invention is particularly useful in radio reception to produce loudspeakers capable of operating on weal; currents, even in circuits that heretofore required telephone headsets for audible reproduction of broadcasting.

Broadly stated, the fundamental idea of my invention comprises a normally balanced magnetic system acting upon a movable magnetic member with opposing magnetic fields hat are normally equal, or substantially so, whereby this member is normally held counterbalanced. This magnetic system may be produced by a permanent magnet or an electromagnet. Combined with the normally balanced magnetic system is a controlling circuit (for instance, a telephone circuit) arranged to unbalance or bias the magnetic system in such a way as to amplify the effects of the controlling current on the magnetic member. As long as the magnetic system remains in equilibrium, the resultant practical effect of its opposing magnetic fields on the movable member is neutral or zero, and the member does not move. However, when a current in the controlling circuit upsets the equilibrium of the magnetic system, the effect of the unbalanced magnetic fields is to cause vibration of the movable member in accordance with current variations in the controlling circuit. The arrangement is such that the unbalancing effect of the controlling circuit on the normally balanced magnetic system is impressed upon the same with amplified intensity. This effect is produced by strengthening one of the fields of the magnetic system in its action on the movable magnetic member and preferably at the same time weakening the other field. The result is an augmented unbalancing of the magnetic system, with a correspondingly strong effect on the movablemember. Accordingly, a power member requiring an elec tric current of certain minimum strength for its proper operation may be controlled by currents too feeble in themselves to operate the member.

According to one form of my invention a normally balanced magnetic system may be obtained by a pair of magnetizing coils connected in parallel paths or branches in an electric circuit, and so mounted on a magn tic frame that the magnetic flux produced by thecurrent in the coils travels in paths or fields of normally equal strength (or substantially so) but of opposite effect. A movable armature is so mounted in relation to these opposing magnetic fields that, as long as the fields are in a state of substantial equilibrium, the armature remains counterbalanced and motionless. If, now, the magnetic field of one coil is strengthened over that of the other coil, the armature will be actuated. This unbalancing of the magnetic fields is effected, by causing the controlling circuit to vary unequally the resistances of the branch circuits containing the coils, preferably decreasing the resistance in one branch and simultaneously increasing it in the other branch. spondingly greater magnetic effect on the armature than the other coil, and the armature is actuated accordingly.

In the broader aspect of my invention, the particular function of the armature is immaterial. For the sake of explaining my invcution. i have selrcte' a construction in which the armature is connected to the acoustic diaphragm of a radio loudspeaker, but it is understood that the armature may control or operate any suitable member. In the accompanying drawings,

Fig. 1 illustrates a loiulspealrer construction in which a movable telephone coil varies certain resistances and thereby controls the relative strength. of magnetic fields acting oppositely and normally with equal effect on a movable armature;

Fig. 2 is an enlarged perspective View of the telephone coil and associated parts of the construction shown in Fig. 1; and

Fig. 8 is a perspective view of an adjustable mounting for the armature of Fig. 1.

Between the poles of a suitable field mag- As a result, one coil has a come.

(iii

net M (of which I need only show the pole' pieces) is mounted an oscillating coil L wound on a suitable frame 1, which may be of aluminum or other light material. lvlagnet M may be a permanent magnet or an electromagnet adapted to provide a substantially constant field of the required strength. The coil frame 1 is provided with a pivot shaitt consisting of aligned pins or spindles 2 and 25, arranged to engage in bearings -1 and 5, re spectively, with as little friction as possible. A pair of oppositely coiled springs (i and 7, preferably of line steel ribbons, normally hold the coil C in the position shown in Fi 1-that is to say, with the plane of the coil substantially parallel with the magne c lines across the air gap of magnet Ill. the coil and its frame can be made very h it, the centering springs 6 and 7 may be cerrespondingly fine, offering a minimum resistance to the movements of coil C in either di rection. If desired, the tension of springs 6 and 7 may be regulated by winding the free ends of the coils around rotatable pins and 9, respectively, which project above the supporting panel 10.

On the lower spindle Z of the coil. :1 1 is lived a contact member consisting pair of conducting arms 11 and arms are preferably of light metal ha Vll some resiliency, so that the outer ends of the arms may contact lirmly with resistance strips 13 and Li, respectively, and yet more over these strii with as little friction as possible. The li 'ht contact between arms ll and 12 and resistance strips 123 and ll a. 1.. the action of springs S a d T to make t oscillating coil C dead-beat. The resestrips 13 and l-l may be of any suitable material (carbon, for instance) adapted to change the resistance of a circuit malenally by a slight movement oi contact arms 11 and 12. It will be understood, of course, that the resistance strips are properly supported in relation to the contact arms ll. and 12. lVhen coil C is in normal position, arms ll and 12 engage the resistance strips at a predetermined point. In Figs. 1 and 2, this normal point ot cnga 'cmcnt is sul. .-.-:tantiall midway of the res.s.anccs. but any other point may be selected, provided that the normal value of the resistances included in the niagnetiziimcircuits is such as to render Ll: circuits of substantially equal and oppor effect on the armature, as will presently explained.

llhe shape of coil frame 1 is prel'crabl such that coil C practically lills the air gap between the poles of magnet ll and mores close to the curved faces of the pole pieces. If desired, a liXed cylinder 15 soitt iron may be arranged in the air gap so as to form a magnetic core about which the coil frame 5 vings a. a. whole. Any suitable means may be provided to hold the core 15 in proper position. The presence of the magnetic core 15 reduces the air gap (and therefore the magnetic reluctance) between the pole pieces to a minimum and thus increases the ell'ect of the magnetic field on coil C when a current passes through the coil. However, core 15 is not absolutely essential.

For convenience, I will refer to coil C as a telephone coil, because I am explaining my invention applied in a radio receiving circuit. This, of course, is merely by way of illustration. In Fig. 1, I have shown coil C connected by a pair of wires 16 to a suitable radio receiving set indicated diagrammatically at R. I need not go into the details of radio set R, since that is no part of my invention and since, moreover, a suitable set maybe purchased in the open market. Also, the proper connection of coil C to radio set R will be understood by those familiar with the radio art.

A reciprocable armature A, consisting of a bar or rod of soft iron or similar magnetic material, is operatively mounted between a pair of magnetizing coils 17 and 18, which I shall briefly call magnet coils to distinguish them from the controlling or telephone coil C, previously referred to. Coils 17 and 18 are connected in parallel paths in the circuit of battery B or other suitable source of direct current. The circuit connections are as fol low: A wire 19 leads from one terminal of the battery to a conductor 20, which connects one end of each coil 17 and 18. A conductor 21 connects the other end of coil 17 with one end of resistance 13. Similarly, the other end of coil 18 is connected to resistance 14: by a wire The other terminal of battery B is connected by a wire 23 to the middle of contact member 111Q. In Fig. 2, I have shown the wire 23 connected to a binding post 24 on a conducting strip 25 leading from the metallic bearing piece 5, with which the arms 11 and 12 are in electrical connection. It is inm'iatcrial how the conductor 23 is electrically connected to the Contact arms 11 and 12. It desired, a variable resistance 26 may be included in the battery circuit to regulate the current rength thereof.

1: will be seen trom the foregoing that coils 17 and 18 are connected in parallel in the battery circuit, with the resistance 13 in the circuit of coil 1'? and resistance 14 in the circuitof coil 18. .Vhen current flows through coils 1? and 18, the magnet field produced by each coil acts to draw armature A into the coil, by virtue of certain laws of electromagnetism which are well understood and need not, therefore, be gone into here. The resistance values of the circuits of coils 17 and 18 are so regulated that normally-that is, when coil C is in the position shown in Fig. 1the oppositely acting magnetic fields of coils 1'7 and 18 are substantially equal and armature A is held in equilibrium. That is to Ill-7 say, the magnetic field of coil 17 normally tends to pull the armature one way as much as the magnetic field of coil 13 tends to pull it the other way, as indicated by the arrows o and w, respectively.

Armature A may be mounted for vibratory movement in any practical way. In Figs. 1 and 3, I have shown one end of the armature carrying a rod or still wire 27, connected to the short arm of a bell-crank 28 pivoted at 29 to a fixed support. The other end of bell-crank 28 is connected to an acoustic diaphragm D of proper construction. The opposite end of armature A carries a screwthreaded rod or extension 30 having a grooved collar 31 adjust-ably mounted thereon. A spring 32 is supported at one end on a bracket and has a bifurcated free end 3 1 engaging in the groove of collar 31. By adjusting this collar axially on rod 30, the normal tension of diaphragm D and spring 32 on armature A may be properly balanced.

Let us now see what happens when a variable current passes through controlling coil C. If we suppose this coil to be included in a talking circuit, the current variations will cause oscillation of the coil in the air gap of magnet M, in accordance with electromagnetic laws which are well understood and require no explanation here. The extent of movement of coil C at any instant depends on the strength of the current passing through the coil, and the direction of movement depends on the direction of current flow, as will be understood. As coil C oscillates, the contact arms 11 and 12 move with it and thus vary the resistances 13 and 14 by increasing one and simultaneously decreasing the other. F or example, let us imagine the coil C in a position in which the contact arms 11 and 12 are in the position indicated by dotted lines 11 and 12 in Fig. 1. The resistance value of resistance member 13h-as been cut down to an amount represented in F 1. by 1', while the active portion of resistance 14 has been simultaneously increased to an amount r. This means that the flow of current through coil 17 is increased, while the flow of current through coil 18 is decreased. Since the magnetizing effect of the coils (cote ris parilnis) depends upon the amperage of the current flowing through them, the may netic field of coil 14' strengtheneda d that of coil 18 weakened, with the result .1 r1uature A is drawn into or toward coil 1i. Th movement. of the arn'iaturo pushes the di. phragm D out. When coil C swings counterclockwise trom its normal position (as viewed in Fig. '1), resistance 13 is increased and resistance 14 decrised, whereby the magnetic field of coil 18 is strengthened and that of coil 1'? weakened. In consequence, the armatureis pulled toward coil 18 and the diaphragm I) is pulled in.

So it will be seen that the vibrations or oscillations of telephone coil C under current variations therein produce an amplified effeet on armature A and, in this instance, on the loudspeaking diaphragm D. In this Way, feeble currents in the circuit of coil C are caused to actuate and control a member which the currents themselves would otherwise be too weak to operate.

While I have herein shown and described a specific construction, I want it understood that my invention is not limited to the details set forth. Changes and modifications may be made without departing from the scopeof the appended claims. In the broad aspect of my invention, the rheostat arm 1112 may be operated in any other practical way to unbalance the magnetic effect of coils 1718, and the movements of member 27 in either direction from its normal positionmay perform any other useful function.

I claim as my invention:

1. In an electromagnetic amplifier, a coil adapted to be connected in a circuit of electric impulses, means for movably mounting said coil in a substantially constant magnetic field, an operative circuit having two parallel branches, electromagnetic means jointly controlled by the currents in said branches, a pair of electric resistance elements connected in said branches, and contact arms movable with said coil for simultaneously increasing the resistance of one of said elements and correspondingly decreasing the resistance of the other element, whereby the movements of said coil control said electromagnetic means in amplified relation to the electric impulses passing through the coil.

2. In an electromagnetic amplifier, a movable coil adapted to be connected in a circuit of variable currents, an operating circuit including a plurality of parallel paths containing each a resistance, means whereby the movements of said coil automatically vary said resistances in different degrees, and a magnetic member controlled by the joint action of said circuit paths.

3. In an electromagnetic amplifier, a controlling coil pivotally mounted in a substantially'constant magnetic field, said coil being adapted to be connected in a circuit of variable currents. an operating circuit including a plurality of parallel paths containing each a resistance, means whereby the movements of said coil automatically vary said resist ances in different 1 degrees, and a magnetic member controlled by the oint action of said circuit paths.

4. In a radio receiving circuit, a loudspeak- 'ing diaphragm, electromagnetic mechanism for operating said diaphragm, said mechanism including a magnet coil, an energizing circuit for said magnet coil. a movable coil mounted in a niagneti field independent of said mechanism and adapted to be connected in the-radio receiving circuit so as to be sulject to current variations in accordance with transmitted impulses, the movements or said last-mentioned coil being in accordance with current variations therein, and means whereby the movements of said coil control the magnetic ellect of said magnet coil to cause vibration of said diaphragn'i in accordance with current variations in said movable coil.

5. In a radio receiving circuit, a pivoted coil mounted in a substantially constant magnetic field and connected in the radio circuit so to be subjected to current variations in accordance with received impulses. the movements of said coil being in accordance with the current variations therein, an electromagnetically operated diaphragm mechanically disconnected from said coil, and means whereby the movements of said coil cause the magnetic elt'ect thereof to be amplified for el ectively operating said diaphragm.

67 In an electroniiagnetic amplifier, a controlling coil pivotally mounted in a substantially constant magnetic field, said coil being adapted to be connected in a circuit of electric impulses, a pair of resistance members adapted to be connected in operative circuits, and contact means movable witn said coil for simultaneously varying the resistance values of said members in inverse ratio to each other.

T. In apparatus of the class described, a pivoted coil mounted in a substantially constant magnetic field and connected in a circuit so as to be subjected to current variations in accordance with received impulses, the movements of said coil being in accordance ith the current variations therein, an electromagnetically operated member mechanically disconnected from said coil, and means whereby the movements of said coil cause the magnetic eti'ect thereof to be amplified for clt'cclively operating said member.

8. ln electric control apparatus, the combination oi" a movable magnetic member, a pair of coils operatively associated with said membe and so connected as to exert opposite electromagnetic ell'ects on said member,- whereby the latter remains in normal position when the opposing electromagnetic effects of said coils are substantially balanced, a rheostat com ected to said coils and having an adjustable contac, arm for disturbing the electromagnetic balance of said coils to produce operation of said meml'ier, the direction of movement of said member depending upon which coil predominates in its electremagnetic action, and operative mechanism controlled by the movements of said member.

9. In electric control apparatus, the combination of a movable magnetic member, a pair of coils surrounding said member and so connected as to exert opposite electromagnetic effects on said member, whereby the latter remains in normal position when the opposing electromagnetic eliects of. said coils are substantially balanced, a rheostat connected to said coils and having a rotary contact arm for disturbing the electromagnetic balance of said coils to produce operation of said member, the direction of movement of said member depending upon which coil predominates in its electromagnetic action, and operative mechanism controlled by the movements of said member.

10. In electric control apparatus, the combination of a movable magnetic member, a pair of coils operatively associated with said member and so connected as to exert opposite electromagnetic effects on said member, whereby the latter remains in normal position when the opposing electromagnetic clfects of said coils are substantially balanced, a rheostat having a pivoted contact arm, means for so connecting said rheostat in the circuit of said coils that the magnetic effect of one coil is increased over that of the other when said arm is moved in either direction from neutral position, this disturbance of the normal electromagnetic balance of said coils causing operation of said member in a direction depending upon which coil predominates, and operative mechanism controlled by the movements of said member, said mechanism including a pivoted element movable in a direction in accordance with the direction of movement of said member.

11. In electric control apparatus, the combination of a pair of solenoid coils, movable magnetic core mechanism operatively ciated with said coils which act in opposite directions on said core mechanism, whereby the direction and extent of movement of said mechanism depend upon the predominating magnetic effect of one coil over the other, a rheostat comprising a pair of resistance elements and a movable contact arm, means for so connecting said coils to said rheostat that the nioven'icnts of said arm increase the resistance in the circuit of one coil and simultaneously decrease the resistance in the circuit of the other coil, so that the movements of said core mechanism correspond to the movements of said contact arm, and an operative member connected to said movable core mechanism.

12. In electric control apparatus, the combination of a pair of solenoid coils, slidable magnetic core mechanism operatively associated with said coils which act in opposite directions on said core mechanism, whereby the direction and extent of movement of said mechanism depend upon the predmninating magnetic effect of one coil over the other, a rheostat comprising circularly arranged resistance means and a pivoted contact arm, means for so connecting said coils to said rheostat that the movements of said arm increase the resistance in the circuit of one coil and simultaneously decrease the resistance in the circuit of the other coil, so that the movements of said core mechanism correspond to the movements of said contact arm, and a pivotally mounted member connected to said movable core mechanism.

13. In electric control apparatus, the combination of a pair of stationary solenoid coils, slidable magnetic core mechanism operatively associated with said coils which act in opposite directions on said core mechanism, whereby the direction and extent of movement of said mechanism depend upon the predominating magnetic efiect of one coil over the other, a rheostat comprising resistance means and a movable contact arm, said rheostat being remotely situated from said coils and mechanism, means for electrically connecting said coils to said rheostat so that the movements of said arm increase the resistance in the circuit of one coil and simultaneously decrease the resistance in the circuit of the other coil, so that the movements of said core mechanism correspond to the movements of said contact arm, and an operative member connected to said slidable core mechanism.

ADOLPH A. THOMAS. 

